designing security measures in VB

I am currently developing an application in VB which requires users to logon. I have created some If statements to take care of repetitive logins, such as administrators, but I would like to be able to have an expandable database so that new users can be recoginized. I also want to tie the login to a second user database that keeps track of certain information that is important in my program. Can anyone give me any ideas, or even better, any lines of code that could accomplush these goals?

Thanks

Colin